This invention relates to a jet for treating yarn from synthetic filaments with heated fluid to introduce random curvilinear crimp. In particular, it relates to a jet for utilizing fluid temperatures above the melt temperature of the synthetic filaments and preventing the filaments from melting on contact with the jet when the yarn is stopped in the jet.
U.S. Pat. No. 3,186,155 discloses that the most effective bulking and greatest productivity of synthetic fibers made from fusible polymer is obtained when the temperature of the heated fluid is above the melting point of the fiber. In this case, the patent teaches, that the yarn speeds should be great enough so that melting does not occur. In such jet bulking processes, the jet body is at a temperature which would cause the filaments to melt and stick to the jet surfaces if they were not moving rapidly. Any process interruption which causes the yarn to stop in the jet may cause the yarn to melt in the jet. The jet must then be removed and cleaned to remove the melted polymer. This procedure is time consuming and costly.